1. Field of the Invention
The present invention relates to utility pole structures constructed of composite materials.
2. Description of Related Art
Utility poles are typically constructed from wooden poles that are anchored into the ground. The utility poles will typically have arms that support a number of electrical power lines. The continuous exposure to harsh environmental conditions can cause the wood poles to rot and decay. To prevent rotting, the wood is sometimes treated with a carbon base material such as tar. It has been found that most conventional wood treating material is harmful to the environment. Additionally, it has been found that a significant amount of electrical current drains to the ground, thereby reducing the energy efficiency of the power system.
Metal poles have been installed to increase the life of the utility poles. Metal poles are highly conductive and generally create an unsafe environment for the utility personnel that maintain and repair the pole. Additionally, both metal and wooden poles are relatively heavy, typically requiring a crane to lift and install the poles.
U.S. Pat. No. 5,175,971 issued to McCombs discloses a hollow utility pole that is constructed from a composite material such as a resin impregnated fiberglass. The McCombs pole has a hexagonally shaped liner located within a hexagonally shaped primary pole. The outer primary pole has a plurality of dove tail grooves that allow arm attachments to be mounted to the pole. Additionally, the grooves allow personnel to climb the pole. The dove tail grooves create a number of rounded fingers located adjacent to thin neck portions of the primary pole.
It has been found that when forming the composite, the resin and glass fibers do not evenly flow into the neck and finger portions of the primary pole. The uneven resin flow and glass fiber distribution can reduce the structural integrity of the pole. The rounded finger portions also add thickness and weight to a utility pole that can be 40 feet in length.
The hollow McComb utility pole has relatively low bending and torsional stiffnesses. The relatively low stiffness must be compensated for by a thicker wall. Increasing the thickness of the wall increases the weight of the pole. It would be desirable to provide a relatively strong, lightweight utility pole which can be efficiently constructed from a composite material.
Composite utility pole structures and methods of manufacture using a pultrusion process. The poles may be N sided, with longitudinal pre-stressed rovings in each corner. The inner periphery of the poles may have flat regions centered between the outside corners, with the flat regions joined by circular arcs in the corner regions. Various pole structures and methods of manufacture are described, including curved poles and poles having walls that are tapered in thickness and structure.